arm: zynq: Fix SPL SD boot mode

This patch is fixing two issues:
1. Insufficient stack size for fat fs buffers
2. Insufficient space in malloc area

Tested on zc702 and zc706.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/configs/zynq_picozed_defconfig b/configs/zynq_picozed_defconfig
index bbccfa5..f36e7bd 100644
--- a/configs/zynq_picozed_defconfig
+++ b/configs/zynq_picozed_defconfig
@@ -1,9 +1,11 @@
 CONFIG_ARM=y
 CONFIG_ARCH_ZYNQ=y
 CONFIG_SYS_TEXT_BASE=0x4000000
+CONFIG_SPL_STACK_R_ADDR=0x200000
 CONFIG_DEFAULT_DEVICE_TREE="zynq-picozed"
 # CONFIG_DISPLAY_CPUINFO is not set
 CONFIG_SPL=y
+CONFIG_SPL_STACK_R=y
 CONFIG_SPL_OS_BOOT=y
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="Zynq> "